Technically he is Lacy’s backup, but just as Richardson proved to be a better all- around talent than Ingram, Yeldon is pushing Lacy for every snap.

This is the two-headed monster Notre Dame’s vaunted defense must stop if it is going to win Monday night’s BCS National Championship game.

Everything the Crimson Tide (12-1) does on offense is predicated on running the ball. Consider: Nick Saban is 49-0 in games in which his team has rushed for 150 yards. The Tide got news yesterday when center Barret Jones, the brains of the offensive line, declared himself ready to play after spraining his foot in a 32-28 win over Georgia in the SEC title game.

So is Notre Dame (12-0). The Irish have a potent run game of their own in George Atkinson III, Theo Riddick and Cierre Wood. And Notre Dame, like ’Bama, must run to win.

Lacy — a 6-foot, 220-pound junior — is a “battering ram,’’ Spencer Tillman, CBS’ studio analyst for College Football Today told The Post.

“He is a linebacker’s dilemma because he would rather run over you than around you,” Tillman said. “He likes contact. He seeks contact.’’

Lacy might have had the quietest successful season of any running back in Alabama history. He rushed for 1,182 yards on 6.42 yards per carry. On any other team, he would have been a Doak Walker Award candidate. On ’Bama, he is the next back in a succession of great ones.

“When you’re playing behind [Richardson and Ingram], you can’t do nothing but learn,’’ Lacy said. “They played on this stage and they played on the next stage as well. Watching them you have to know to be poised and know that things are not going to go right all the time.’’

It went right for Lacy in the SEC title game. He was named the MVP after gouging Georgia for 181 of the Tide’s 350 rushing yards. He averaged 9.1 yards per rush. He battered Georgia into submission, and that will be his mission against Notre Dame.

Yeldon is a 6-2, 216-pound freshman.

“He’s the closer,’’ Tillman said. “Yes, he’s physical like Lacy, has power, but he has the change up, that step. Alabama feeds you Lacy, Lacy, Lacy, and then it’s Yeldon and he breaks it.’’

Yeldon was Mr. Football in Alabama and initially committed to Auburn before flipping to the Tide, which sparked a holy war in the state. Auburn message boards lit up with accusations Alabama paid to get Yeldon. Cam Newton had no comment.

Yeldon needed exactly one game to make Auburn fans regret his change of heart. In the opener against Michigan, Yeldon became the first back in Alabama history to rush for more than 100 yards in his debut. He busted the Wolverines for 111 yards on 11 carries.

First he started a brushfire in state, then he started a coffee-shop debate in Tuscaloosa: “How soon before Yeldon became the feature back?” Lacy started every game. But Yeldon actually finished with a slightly better yards per average (6.5) while rushing for an even 1,000 yards.

“Alabama’s running backs are tremendous,’’ Notre Dame defensive end Kapron Lewis-Moore said. “Yeldon is the guy who is a jump-out runner, while Lacy is not going to hit you with moves and is going to cram for those extra yards.’’

The two-headed monster mainly is responsible for Alabama averaging 224 yards per game on the ground, 19th in the nation. The Tide scored 35 rushing touchdowns.

“As a team, we’re relentless,” Lacy said.

Notre Dame was fourth in the nation against the rush, allowing just 92.4 yards. The Irish allowed a mere two rushing touchdowns all season. Something’s got to give.